View topic - Fluid Drive on a 47

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Hello i recently got my hands on a 47 DeSoto with fluid drive and i dont quite understand it from what Im reading 10 wt motor oil goes in somewhere and ATF goes in somewhere else ? is this right ? Also who sells 10 WT motor oil? Ive been having trouble finding that as well .thanks everyone

The Fluid Drive is checked for content, added to andre-filled at the location number three. You may use ATF ifyou plan on locating ( finding ) and replacing the seals this coming summer. Use Hydraulic Fluid # 134 or an like fluid.

****************************************************The Fluid the era writings say to use is no longer with us.The Hydraulic Fluid #134 is very near it "lab wise".****************************************************

Since ATF may have been placed in the unit or the unitmay be in need of a "fresh supply", it may be a good timeto drain the old and replace with Hydraulic Fluid # 134.

It is the transmission ( location # 4 ) that uses the 10w engine motor oil.

Either of these will not be found at Walmart and the like.You will need to shop at NAPA, a Farm suply/repair place orstop at any local to you Fuel Supply.

Michael, DON'T put ATF in your DeSoto. The transmision and the fluid coupling both use 10 wt non-detergent motor oil. Roger is right about the #134 hydraulic fluid it works just as well as 10 wt. oil. I have had it in my 52 for several years and several thousand miles with no problems. You can get the hydraulic fluid at any farm supply store. I have also seen the 10 wt.oil at our local farm supply. The fluid coupling seldom needs filled so it is probably OK unless someone has drained it or you just want to change the fluid.

Technical Note on MOPAR Fluid Couplings (Fluid Torque Couplings are NOT covered by this Technical Note)By James Douglas – San Francisco (2009)

Having run several types of oil in MOPAR “Fluid Couplings” over the years and heard many recommendations, I decided to see if I could approach the issue of what lubricant to use in one of MOPAR’s Fluid Couplings by a more scientific method.

As is well known, Chrysler instructed all owners to use “MOPAR Fluid Drive Fluid” only in their Fluid Couplings. Problem is, MOPAR stopped making it decades ago.

My first stop was Chrysler Historical. After a month of looking, I was told that they do not have any of the original engineering information as to the specifications of the fluid.

Then I headed off into internet land to hunt down anything I could find on the subject from ORIGINAL sources. I managed to find an original Chrysler Question and Answer sheet from 1939 about fluid drive from Chrysler Engineering. In it they stated:

“…The proper fluid is a low viscosity mineral oil, which also servers to lubricate the bearing enclosed in the coupling. The pour point is such that the oil will pour at the lowest anticipated temperature, and has no corrosive effect on the steel parts of the unit.”

All well and nice, but not enough to figure out exactly what they used as fluid. Later in the same document they talk about the types of metal used and the carbon-graphite seal. Hum, carbon-graphite seal.

I did some more digging for a few months and turned up a can of unopened original MOPAR Fluid Drive Oil.

An analysis of that oil, and some more literature I ran across, stated that the original fluid was a pure-base mineral oil with a Saybolt Viscosity of between 100 and 150. The fluid had a Viscosity Index (NOT the same thing a general viscosity) of greater than 80.

The fluid had anti-foaming and anti-oxidation additives. It specifically did NOT have any seal swelling agents as these can attack the carbon-graphite seal and the copper in the bellows. This last specification eliminates most modern transmission fluids.

After finding several formulas to convert Saybolt Viscosities to Kinematic Viscosities, it appears that the best match to the original specification is ISO 22 or ISO 32 oil.

However, the ISO 22 is just below 100 Saybolt and the ISO 32 is much higher than 100 Saybolt.

Based on a period (c.1947) Lubrication Industry article on fluid couplings that had the following admonishment:

“Contrary to popular supposition any attempt to use a higher viscosity fluid would actually reduce the torque transmitting ability of the coupling since torque-transmission is dependent upon a high circulation of fluid between the impeller and runner and is not caused by any viscous drag between the two.”

During my continued research on the history of the Fluid Coupling, I ran across the fact that the original company that licensed the fluid coupling technology to Chrysler is still in business and still making fluid couplings for industrial applications.

After a couple of weeks of digging, I found a senior engineer from that company that would have a long technical talk with me on fluid couplings. In essence, he agreed with the period information I quoted above. He added that the lowest viscosity oil that would still provide for bearing lubrication is the one to use in theory. However, he did say that unless the fluid coupling bearing has been replaced and is know to be very high quality then err on the heavy side viscosity wise. Just don’t over do it, he stated.

I was also told that normal hydraulic fluid does not have large amounts of anti-foaming agents in them as they usually do not have large amounts of air in the systems to foam in the first place.

A fluid coupling is only filled to 80% and as such has lots of air in it.

Therefore, when looking for fluid coupling oil, one must look for an oil that is a “Circulating Oil” which has a lot of anti-foaming additives in it.

I was also informed that the additives tend to have a shelf life in the can, or in use, of 5 to 7 years and it should be changed at that time.

I was also told that the couplings are actually somewhat permeable and water vapor will work its way into and then back out, when hot, of a steel fluid coupling. Very little amounts, but apparently is does go on.

I was also told to never use engine oil or ATF as both would cause problems in the long run.

Based on the research and discussions I have come to the conclusion that ISO 32 hydraulic oil with the proper additives and VI (Viscosity Index) above 80 is a suitable replacement for the original MOPAR fluid drive fluid. ISO 22 would be a better exact match, but only if the quality and condition of the bearing is know in a particular coupling.

The oil I have identified that meets the specification, with a higher general viscosity to deal with the age of the bearings, is: Mobile DTE light circulating oil ISO 32. This oil is available at Granger.

I have run this oil for about six months in San Francisco city traffic as well as up steep mountains on very hot days. The coupling works well. I have noticed, and other car people have as well, that the car seems to move out from a dead stop to 10 MPH better with the fluid. Only a before and after session on a dynamometer would tell for sure, but I feel that it moves out much faster.

Classic car owners are advised to use this information at their own risk. I am not a fluid coupling engineer, a bearing engineer, or a lubrication engineer. I have done my best to find out what was in the original MOPAR Fluid Drive Fluid. This effort is in essence industrial archeology and should be carefully considered prior to use.

************* The text in this article is the property of James Douglas. It may be copied and passed on or reprinted only on the condition that it is copied in its entirety and attributed to James Douglas.************

I've heard that "tractor fluid" is a suitable substitute for the fluid drive. I'm not an expert on fluid drive, but I have plenty of tractor fluid experience. It is both light enough to operate tractor hydraulic systems and serve as the medium in torque converters and hydrostatic drives and is also a good lubricant for transmission gearing.

It (Tractor Fluid) does not have enough anti-foaming additives. There are two basic kinds of hydraulic fluid. Static fluid used in hydraulic cylinders and hydraulic fluid that flows through systems that have a lot of air in them. The fluid couplings need the second.

As a technically oriented person myself, I would have to say that James has assessed many of the important aspects of the oil needed in the coupling. Very good job James. I found the 10W non detergent oil from a place in CA. It is motor oil but seems to work fine but I may have to look at it again. I wonder if James knows the reason not to use engine/motor oil.

As a technically oriented person myself, I would have to say that James has assessed many of the important aspects of the oil needed in the coupling. Very good job James. I found the 10W non detergent oil from a place in CA. It is motor oil but seems to work fine but I may have to look at it again. I wonder if James knows the reason not to use engine/motor oil.

Motor Oil has almost no anti-foaming properties. It also has a VERY limited VI.

The thing that many people don't appreciate is that a torque converter and fluid coupling differ in one very big way. That is that a fluid coupling has about 20% air in it where a torque converter is about full.

That is a big deal in that the air will cause the coupling oil to froth. Since it is the velocity of the fluid not the viscosity of the fluid that makes the car go...that frothing robs you of power particularly during take off.

The analysis of the original fluid and the conversation with the folks at Gyrol confirm the need for a anti-foaming agent. The problem is that the anti-foaming agent costs more so the fluid costs more. Also, the stuff breaks down after about 6-8 years. This last item is interesting.

Most people did not bitch too much about the acceleration when the fluid drive cars were new. I think that the anti foaming agents degraded and so the low end take off deteriorated. I know that when I put the stuff into my car the acceleration was noticeably improved and that was the only change.

The mobile circulating fluid is available at Granger. I have no doubt that tractor fluid will work. But it is not what MOPAR specified and it is not what Gyrol specifies. MOPAR licensed the coupling technology from Gyrol so they should know what they are talking about.

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